Rayburn water overheating problem



Hi all, hope someone can help with this little Rayburn heating query.

Our 2 storey house has a gas-fired Rayburn on the ground floor in a central location, and on the first floor above it is the hot water cylinder which it heats. The thermostat knob on the side of the Rayburn for the central heating, has settings from off to 80, but we always have it set to "off". Just along from the Rayburn behind a panel is a central heating pump, which in turn is connected via a Honeywell dial-style roomstat, to a Lifestyle LP722 digital timer. Been in this house several years now, first one we've lived in with a Rayburn, and I'm not sure whether what we are experiencing with our central heating is as to be expected, whether something is maybe incorrectly wired or plumbed in, or whether it's just me not understanding how it works. It's been bothering me for a couple of years since we had our kitchen re-fitted.

The LP722 has 4 states, off, twice, once, or on, for each of hot water and central heating, so you can have either the hot water or the CH in any of the four settings. Over the summer we have the timer set to off for both, in fact the HW side is set to off all year. We still have warm-to-hot water on tap in these months, but sometimes after we have had a lot of usage (e.g. baths) in the summer, we have to switch the timer to "twice" (and tolerate a little summer central heating) for a day or so to get the water temperature back up quickly. Even in the summer, with the LP722 set to "off", the radiators upstairs, closest to the water cylinder, still have a little heat in them unless we shut them off.

When it gets to the winter, about now, we put the LP722 on "twice" for the central heating, with the timer set for a couple of hours in the morning and about 6 hrs in the evening. Rayburn thermostat and HW side of LP722 still set to "off". CH seems to work OK no problem, turn the roomstat to the point where you hear the click, and you can hear the Rayburn light and the pump kicks in. However the hot water is being massively heated. Particularly in the mornings and later in the evening, the pipework around the Rayburn is banging away, very hot water comes out of the taps, and you can hear water bubbling ferociously inside the Rayburn.

So we have to turn the LP722 to "off" (and thus shut off the central heating) just to calm down the hot water situation. This overheating of the water seems to build up even when the LP722 is set to "twice" but is not within a timer-on period (i.e. its red lights are off).

So this kind of defeats the object of having the LP722, because in using it to control when the house is heated, it so overheats the water we have to operate the CH timing manually. Even with the HW side of the LP722 set to off, and the thermostat on the side of the Rayburn set to off as well. It's probably costing us more in gas usage than it needs to as well. Can anybody shed any light on what might be going on here - something wrongly wired or plumbed, or is all of this just normal Rayburn performance?
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10 Jun 2009
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United Kingdom
Suspect you have a stuck motorised valve on your Hot Water cylinder coil, as far as I can remember Gas Rayburns are fully automatic and do not need a heat leak connected to them, so the system should operate in exactly the same way as a standard gas fired heating system ;)


Thanks for the info, what job does the motorised valve do, and whereabouts might I find it? Can they be "unstuck" or is it a case of getting a new one installed? Presumably it's something a local plumber can do or would it need a Rayburn specialist?

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